1. Field of the Invention
The present invention relates to a solid-state image capturing apparatus having semiconductor devices for performing photoelectric conversion on image light from a subject to capture the same, and more particularly, to a solid-state image capturing apparatus suitable for minimizing a cell size, and an electronic information device, such as a digital camera (e.g., digital video camera and digital still camera), an image input camera, a scanner, a facsimile machine and a camera-equipped cell phone device, having the solid-state image capturing apparatus as an image input device in an image capturing section of the electronic information device.
2. Description of the Related Art
In recent years, solid-state image capturing apparatuses used for digital still cameras, digital video cameras and the like steadily continue to be reduced in size and to have a higher pixel density. With respect to CCD solid-state image capturing apparatus, which is one type of the solid-state image capturing apparatuses, because of the reducing of size and the increasing of pixel density of the image capturing apparatus, its cell size has been minimized, and in addition, the cell size of a light receiving section and a vertical charge transfer register has been further minimized. Such a reduction in size leads to a decrease in light receiving sensitivity, a decrease in the capacity to store electric charges in a light receiving section, and a decrease in the capacity to store vertical charge transfer in a vertical charge transfer register. Therefore it is becoming difficult to achieve further minimization.
Herein, the structure of a conventional solid-state image capturing apparatus will be described in detail with reference to FIG. 9.
FIG. 9 is a block diagram schematically showing an exemplary diagrammatic structure of a conventional solid-state image capturing apparatus.
In FIG. 9, the structure of a conventional solid-state image capturing apparatus 100 is divided into an image capturing section 101 provided with a plurality of pixel sections, a horizontal charge transfer register 102 for transferring signal charges from the image capturing section 101 in a horizontal direction, and a signal output section 103 functioning as an electric charge detection section for detecting the transferred signal charges to output them as image capturing signals.
In the image capturing section 101, a plurality of light receiving sections 104, which is formed of a plurality of pixel sections for performing photoelectric conversion and storing generated signal charges, are arranged in a matrix in row and column directions (vertical and horizontal directions). Along each column of the respective light receiving sections 104, a vertical charge transfer register 105 is provided to transfer signal charges in a vertical direction.
According to the structure described above, first, image light from a subject enters the plurality of light receiving sections 104. Each of the light receiving sections 104 performs photoelectric conversion on the incident light to generate signal charges, and the signal charges are stored. Next, the signal charges in each pixel column are transferred in a vertical direction by each vertical charge transfer register 105. The transferred electric charges in each pixel row are transferred in a horizontal direction to the signal output section 103 by the horizontal charge transfer register 102. Further, the transferred signal charges are detected by the signal output section 103 and are outputted as image capturing signals.
The structure of a vertical charge transfer electrode in the conventional solid-state image capturing apparatus will be described in detail with reference to FIG. 10.
FIG. 10 is a top view showing an exemplary essential structure of an image capturing section in the solid-state image capturing apparatus 100 in FIG. 9.
In FIG. 10, the vertical charge transfer register 105 in the conventional solid-state image capturing apparatus 100 is provided in between light receiving sections 104 in a column direction, and a first layer of a vertical transfer electrode 106 and a second layer of a vertical transfer electrode 107, which are composed of a polysilicon film and are respectively interposed by a insulation film, are successively arranged on the vertical charge transfer register 105. The two types of the vertical transfer electrodes 106 and 107 are alternatively arranged on the vertical charge transfer register 105 in a charge transfer direction, and the vertical transfer electrode 107 is provided for each light receiving section 104 in an adjacent manner. The second layer of the vertical charge transfer register 107 is arranged in a corresponding manner to the vertical width of the light receiving section 104. The vertical transfer electrode 107 also serves as a readout electrode for reading signal charges from the light receiving section 104 to the vertical charge transfer register 105.
With the structure described above, the conventional solid-state image capturing apparatus 100 operates as follows.
First, image light from a subject enters each of the light receiving sections 104 and the incident light is photoelectrically converted into signal charges. The signal charges are once stored in each of the light receiving sections 104, the light receiving sections forming respective pixel sections.
Next, the signal charges stored in the respective light receiving sections 104 are read out to the sides of the respective vertical charge transfer registers 105 in each pixel column by the respective readout electrodes 107.
Further, the signal charges, which are read out by the respective vertical charge transfer registers 105 in each column, are transferred to the horizontal charge transfer registers 102 side by one horizontal line at a time in a vertical direction in the respective pixel sections corresponding to a display screen.
The signal charges in each pixel row (one horizontal line), which are transferred to the horizontal charge transfer register 102, are transferred in a horizontal direction to the signal output section 103 and are detected in the signal output section 103 to be outputted as image capturing signals for respective pixels.
As described above, it is necessary to reduce the size of the conventional solid-state image capturing apparatus 100 as much as possible in order to obtain a small and high pixel density conventional solid-state image capturing apparatus 100. In order to reduce the size and increase the pixel density, it is necessary to minimize the cell size of the image capturing apparatus. Thus, it is necessary to minimize the light receiving section and the vertical charge transfer register themselves in order to minimize the cell size. However, openings (openings above the light receiving section 104) of a shading film covering the vertical transfer electrode becomes narrow if the cell size is minimized, causing the decrease in light receiving sensitivity and the decrease in dynamic range.
As shown in FIG. 11, Reference 1 discloses a solid-state image capturing apparatus 110, in which light receiving sections 104a and 104b are arranged on either side of a vertical charge transfer register 105 and the light receiving sections 104a and 104b are repeatedly arranged in parallel to each other. The light receiving section 104a arranged on the right side of the vertical transfer register 105 and the light receiving section 104b arranged on the left side of another vertical transfer register 105 adjacent to the right of the aforesaid vertical transfer register 105 are separated by a separation area (channel stop area) 108. Due to the pixel separation structure, it is feasible to minimize the area of the vertical charge transfer register 105 and increase the area of the light receiving section 104, thereby preventing the light receiving sensitivity and the dynamic range from decreasing.
As shown in FIG. 12, Reference 2 discloses a solid-state image capturing apparatus 120, in which light receiving sections 104a and 104b are arranged on both of the left and right sides of a vertical transfer register 105 and the positions of the light receiving sections 104a and 104b are shifted from each other in a vertical transfer direction. In this case, the light receiving section 104a on one side generates signal charges to be outputted during a first field period, and the light receiving section 104b on the other side generates signal charges to be outputted during a second field period. Due to this structure, the resolution can be improved by increasing the number of the light receiving sections 104a and 104b in a specific direction such as a vertical direction.
Reference 1: Japanese Laid-Open Publication No. 5-344425
Reference 2: Japanese Laid-Open Publication No. 62-155560